1. Field of the Invention
The present invention relates to an alternator that is provided with a rectifier which is mounted, for example, on a vehicle for rectifying an alternating current generated in a stator coil of a stator into a direct current.
2. Description of the Related Art
In the past, in an alternator for a vehicle as described in a first patent document (Japanese patent 4020211, paragraphs 0010-0013 and FIG. 2 through FIG. 4), incorporated herein by reference, there is provided a rectifier 12 that is electrically connected to a stator coil 16 for rectifying an alternating current generated in the stator coil 16 into a direct current. The rectifier 12 includes a plurality of diodes 23, 25 that form a full-wave rectifier circuit, a negative terminal side heat sink 26 and a positive terminal side heat sink 24 that serve to hold these diodes 23, 25, respectively, and a circuit board 20 that serves to make electrical connections between the diodes 23, 25 and the stator coil 16, wherein the negative terminal side heat sink 26, the positive terminal side heat sink 24 and the circuit board 20 are mounted on a casing 3 at three mounting portions 20a, 20b, 20c, which are superposed with one another in an axial direction of a shaft 6, by the use of screws 40.
In this case, the circuit board 20 of the rectifier 12 is arranged in a bridge state between two points of the mounting portions 20a, 20b, 20c, and vibration suppression portions 20ab, 20ac, each having a thickness larger than that of each of the mounting portions 20a, 20b, 20c, are provided on the mounting portions 20a, 20b, 20c so as to reduce the easiness or frequency of occurrence of a vibration mode. As a result, the occurrence of the vibration mode of the circuit board 20 between the above-mentioned two points can be suppressed.
In addition, in a rectifier of a vehicular alternator as described in a second patent document (Japanese patent 3826775, paragraph 0022 and FIG. 5), incorporated herein by reference, a fastening metal fitting 58 with a female threaded portion 59 formed therein is inserted in a terminal block 50, and a through hole 44 is formed in a region of a positive terminal side cooling fin 42 at a location opposing the fastening metal fitting 58, wherein a fastening bolt 70 is caused to extend or penetrate into the through hole 44 in the positive terminal side cooling fin 42 to be placed into threaded engagement with the female threaded portion 59 of the fastening metal fitting 58, whereby the positive terminal side cooling fin 42 and the terminal block 50 are fixedly connected with each other.
As shown in FIG. 3 of the above-mentioned first patent document, in this rectifier 12, each of the first insulating members 41 is of a cylindrical shape and has a flange interposed between the negative terminal side heat sink 26 and the positive terminal side heat sink 24. The circuit board 20, the positive terminal side heat sink 24 and the negative terminal side heat sink 26 are formed or assembled into an integral unit by causing second insulating members 42, each of which takes a cylindrical shape and has a flange, to extend through holes in the first insulating members 41 and the positive terminal side heat sink 24 and holes in the mounting portions 20a, 20b, 20c. 
Further, the rectifier 12 thus integrally assembled is fixedly secured to a rear bracket 2 by causing the screws 40 to penetrate or extend through the respective second insulating members 42 to be threaded with the rear bracket 2.
The flanges of the first insulating members 41 are sandwiched between the negative terminal side heat sink 26 and the positive terminal side heat sink 24 which are both made of aluminum and hence have thermal expansion coefficients different from that of the first insulating members 41. As a result, in case where the alternator is mounted on a vehicle and used under an environment in which the temperature of the alternator changes from −40 degrees C. to 120 degrees C, the mutual connection or coupling of the circuit board 20, the positive terminal side heat sink 24, and the negative terminal side heat sink 26 often becomes unstable.
Therefore, there has been a problem that vibration applied to the alternator when it is mounted on the vehicle might directly cause damage or breakage in the connecting portions of the diodes 23, 25 and the circuit board 20.
In addition, the vibration suppression portions 20ab, 20ac provided on the rectifier 12 are larger in thickness than the mounting portions 20a, 20b, 20c, so there has also been another problem that the weight of the circuit board 20 itself is increased, giving rise to a feat that the increased weight might be applied to the above-mentioned connecting portions.
Also in the above-mentioned second patent document, the through hole 44 is formed in the positive terminal side cooling fin 42 that will have potential, and the fastening bolt 70 is penetrated or extended through the through hole 44 and is then coupled to the fastening metal fitting 58, so there has been a further problem that partial discharge might occur under a use environment in which foreign matter is liable to be attached to the positive terminal side cooling fin 42.
Furthermore, because the fastening metal fitting 58 is inserted into the terminal block 50, and a through hole 36 for coupling operation of the fastening bolt 70 is formed in the negative terminal side cooling fin 32, there has been a still further problem that a complicated structure results, too.